With many types of refuse burning furnaces, especially those burning waste liquor produced when pulping wood, the combustion air is supplied through a comparatively large number of ports located at different levels in the furnace walls.
Air distribution boxes are fitted outside of the walls. An air box is usually subdivided into sections, each feeding a certain number of ports and being provided with throttling means for governing the flow of air. Especially with furnaces burning wood pulping waste liquor it is essential to be able to maintain the air pressure within the section, and thereby the velocity of the air flowing out of the port, within certain, predetermined levels.
In order to attain this it is, however, not sufficient to govern the air flow solely by the throttling means, but each port ought to have a governing member located as close to its mouth as is practically possible.
In this manner, the size of the passage opening may be adjusted individually at each port, so the desired velocity is obtained at the mouth of the port. By the throttling means, the air pressure within the air box section is determined with respect to the desired outflow velocity and thus also the total volume of air.
With refuse burning furnaces, and especially those of the pulping industry, thick deposits will be formed on the inward faces of the furnace walls, which brings about special difficulties with respect to the individual governing of the passage areas at the individual ports. As has been mentioned above, the governing member is located as close to the mouth of the port as is possible in order to obtain the desired result, viz. to maintain the flow velocity with varying volumes of air.
The location of the governing member so close by the mouth of the passage implies a risk that droplets of slag running down the wall, or being carried by the turbulent gases, are thrown into the port, where they will clog the governing means. This is cooled by the air flowing through the port, so the governing member will soon be completely cemented to the walls of the port and must be mechanically chopped free when an adjustment is to be performed.
It is evident that this type of governing means is not well suited for automatic operation, and therefore the adjustment has to be done manually. Manual attention to so many governing means as are provided in a refuse burning furnace cannot be made as rapidly as is desirable in order to obtain the best combustion results.